Small Cell Mobile Backhaul: The LTE Capacity Shortfall

• June 22, 2011
• 3GPP Long Term Evolution, Aviat Networks, Backhaul (telecommunications), Business, Capital expenditure, Gary Croke, mobile broadband, Mobile network operator, Product Marketing Manager, Services, spectral efficiency, Telecommunication, wireless

With immense mass-market demand for mobile broadband services, and emergence of new high-capacity mobile devices (e.g., smartphones, tablets) and applications, many of the world’s most advanced mobile networks are struggling to deliver a high-quality consumer experience. Explosion of per-user data consumption, combined with subscriber growth and mobility needs, is putting today’s networks are under tremendous pressure. In addition, as operators continuously evolve networks with the latest technology (e.g., 2G, 3G, 4G) to meet these capacity and coverage demands, network costs are exploding and operators are struggling to keep up profitable businesses.

LTE, representing a 4x capacity improvement over current 3G networks, on its own will be insufficient to address all future capacity demands, as mobile data traffic will double every year equating to a 32x growth by 2014 (Figure 1).

Figure 1: The forecast 32x jump in data demand cannot be met alone by LTE, which can only offer a 4x increase over current wireless technologies.

Increasing spectral efficiency with new versions of LTE will help manage the shortfall, but these solutions are not yet available and again will not provide the volume of capacity necessary. Acquiring more spectrum would help but additional spectrum is costly and in most cases not available. Traffic management approaches such as caching and mobile data offloading are emerging to help manage the load but because of limited cache hit rates, these solutions will be insufficient to address the capacity shortfall. Offload techniques, such as in-home femto cells and mobile offload gateways, are emerging to reduce load on mobile infrastructure, but again they will be insufficient. A new approach is required.

Emergence of Small Cells

To meet these capacity challenges, and address ever-prevalent coverage issues, new small cell network architectures are emerging based on a new generation of low power, small cell (i.e., micro, pico, femto) mobile base stations. ABI Research estimates 4 million pico base stations will be shipped per year by 2015. Being deployed into an existing network on lampposts, utility poles and building walls, these base stations offer a way for operators to meet challenges of urban, suburban and in-building locations. Combined with existing base station infrastructure, these small cells are transforming the flat macro mobile network into a multi-level, hierarchical radio access network (Figure 2).

Figure 2: Combined with existing macro base station infrastructure, small cells are transforming the flat mobile network into a multi-level, hierarchical radio access network.

Small Cell Backhaul: Wired or Wireless

When considering IP mobile backhaul options, operators must first ponder the choice between wireline or wireless solutions. There is generally no “one-size-fits-all” solution, and in reality we’re likely to see a mix of mobile backhaul technologies deployed to meet the small cell backhaul challenge. However, because of challenging utility pole and lamppost deployments, operators cannot count on fixed line options (e.g., fiber, cable, copper/DSL) being ubiquitously available. Moreover, more than 40 percent of the world’s macrocell base stations are backhauled wirelessly and because of these challenging locations, we’re likely to see a much higher percentage of wireless-based backhaul in small cell applications.

Wireless Backhaul for Small Cells: Challenges

Small cell deployments present a number of challenges—not the least of which is impact on mobile backhaul. Operators—and equipment vendors—must consider the key factors below when selecting (and designing) wireless backhaul solutions for small cells:

• Lower cost solutions needed—Smaller cells mean more cells and thus more mobile backhaul. To meet overall cost objectives, lower cost backhaul solutions will be required to make sure small cells can be deployed cost effectively. Typical macrocell backhaul CapEx is about 50 percent of the total base station CapEx, and similar ratios will be required to ensure a cost-effective solution.

• Space-optimized solutions required—To improve street-level coverage and capacity, small cells are being deployed on lampposts and utility poles. These challenging deployment locations place demands on the physical attributes of backhaul solutions. Unlike traditional cellsites, typical dish antennas will not be feasible for such deployments. In addition, because of space constraints and operations costs, backhaul and base station hardware integrated into common enclosures would be ideal.

• Line-of-Sight (LOS) not possible—Street level, metro area deployments mean line of sight to backhaul hub locations are not always—in fact—rarely possible. Requiring large antennas, combined with lack of LOS characteristics, makes traditional point-to-point wireless backhaul ineffective for most small cell backhaul applications.

• Interference must be carefully managed—When it comes to wireless backhaul solutions, close proximity of cellsites creates possible interference issues for the backhaul system. These interference issues are relatively new for backhaul systems and need to be considered.

• High-capacity solutions required—Driven by increasing demand for mobile data, backhaul requirements for small cells are expected to approach macro cell capacity requirements (50-100Mbps per cellsite) in the next three years.

Which challenges matter most will depend heavily on how small cells eventually are deployed. Stay tuned for a followup blog post where I discuss small cell backhaul deployment options and available solutions to address these needs. In the meantime, feel free to leave me your thoughts, or comments.

Gary Croke
Sr. Product Marketing Manager, Aviat Networks

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